- Email: [email protected]
Bone metabolism and energy balance: role for leptin◊
Joint Bone Spine 72 (2005) 471–473 http://france.elsevier.com/direct/BONSOI/
Research lecture
Bone metabolism and energy balance: role for leptin◊ Thierry Thomas *, Aline Martin Inserm E0366, Rheumatology Department, Saint-Etienne Teaching Hospital, Boulevard Pasteur, 42055 Saint-Etienne Cedex 02, France Received 5 October 2005; accepted 6 October 2005 Available online 25 October 2005
Keywords: Leptin; Osteoblast; Osteoclast; RANKL; Obesity
Both obesity and osteoporosis are major public health issues in their own right. Leptin seems to mediate the protective effects of fat mass on bone. This 16-kDa product of the ob gene is produced primarily by white adipose tissue, and its plasma levels are closely correlated with fat mass. Leptin has generated considerable interest as a marker for energy status. [1] Independently from the central appetite-regulating loop, leptin acts on most of the endocrine pathways not only via the hypothalamopituitary axis, but also directly on peripheral endocrine glands [2]. Leptin deficiency leads to multiple phenotypic abnormalities in addition to obesity, establishing a pleiotropic role for this hormone, which is involved in regulating many physiological processes including bone metabolism [3]. Thomas et al. [4] followed by other groups [5,6] showed that cells of osteoblast lineage, whether precursor stromal cells or more mature osteoblasts, constitute a target for leptin, as they express the long and short forms of the leptin receptor, whose activation generates a signal via STAT3 phosphorylation [7]. In vitro studies established that leptin induced MAPK-dependent proliferation of murine C3H10T1/2 multipotent stromal cells [8] and of osteoblasts at a more differentiated stage [6]. Furthermore, leptin enhances the osteoblastic differentiation of human stromal cells, inducing increased mineralization of the extracellular matrix. [4] Similar findings have been obtained with other cell models [5,9,10]. In vivo, intraperitoneal leptin injections reduced the bone loss caused by estrogen deprivation in ovariectomized rats [11]. In addition, daily systemic administration of leptin to sexually mature male mice *
Corresponding author. Tel.: +33 4 77 12 76 49; fax: +33 4 77 12 75 77. E-mail address: [email protected] (T. Thomas). ◊ Lecture held on the occasion of the 18th French Congress for Rheumatology. 1297-319X/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.jbspin.2005.10.005
was followed by a greater than 20% increase in mechanical bone strength [6]. These beneficial effects on bone may depend, at least in part, on the ability of leptin to reciprocally modulate stromal cell differentiation toward osteoblasts and adipose cells, inhibiting adipogenesis via a negative feedback loop operating in parallel with the osteoblast-stimulating effects [4,12]. However, in animals with leptin pathway abnormalities (absence of leptin or leptin-receptor mutations), the effects of leptin on bone described are conflicting and are at times inconsistent with the in vitro and in vivo effects discussed above. Steppan et al. [13] reported decreased bone mineral content (BMC) and bone mineral density (BMD) values at the whole body and femur of ob/ob mice, which lack leptin, suggesting a beneficial effect of leptin on bone. However, in a study by Ducy et al. [14] a high bone mass phenotype was found in ob/ob mice. Lorentzon et al. [15] reported that db/db mice lacking functional leptin receptors had osteopenia with thinning of the femoral cortex and loss of trabeculae compared to normal mice, whereas Ducy et al. [14] concluded that bone mass was noticeably increased in db/db mice compared to wild-type mice. Zucker fa/fa rats, which are obese and lack functional leptin receptors, were reported by Foldes et al. [16] and Mathey et al. [17] to have decreased BMC and BMD values at the total femur, femoral diaphysis and femoral metaphysis, compared to normal rats. On the other hand, Schilling et al. [18] reported a high bone mass phenotype in Zucker rats similar to that seen in ob/ob mice. These discrepancies may be partly ascribable to bone phenotype differences between the axial and the peripheral skeleton [19]. Ducy et al. [14] showed that intracerebroventricular leptin injections were followed by a decrease in bone density, both in ob/ob mice and in wild-type mice [20]. This leptin-dependent
472
T. Thomas, A. Martin / Joint Bone Spine 72 (2005) 471–473
central inhibition of bone formation is mediated by the sympathetic system [21] that acts directly on osteoblasts expressing the β2 adrenoceptor [22,23]. Other studies in ob/ob mice showed that intraperitoneal leptin induced a major increase in cortical bone formation [24] an increase in endosteal bone formation with a decrease in the concentration of bone marrow adipocytes [25] and correction of the osteopenia and bone growth deficiency characteristic of the ob/ob phenotype, compared to controls, despite decreases in food intake and body weight [13]. Leptin may control the activity of osteoclasts, which constitute another potential cell target. Leptin can modulate the RANKL/osteoprotegerin (OPG) ratio by inhibiting RANKL expression and stimulating OPG expression in preosteoblastic stromal cells [11] and circulating mononuclear cells [26]. There is conclusive evidence that the RANKL/OPG ratio is crucial to the control of osteoclastogenesis. RANKL expressed by osteoblastic cells binds to RANK at the surface of preosteoclasts and of osteoclasts at a more mature stage, stimulating their differentiation, maintaining their activity, and inhibiting their apoptosis. OPG, which is also expressed by osteoblasts, acts as a soluble receptor that prevents RANKL from binding to RANK. This dual effect of leptin, with inhibition of bone resorption and stimulation of bone formation, was recently confirmed in vivo in an animal model of immobility-induced osteoporosis, in which the RANKL/OPG ratio within bone tissue returned to normal [27]. Again, results from different models seem to contradict one another. Thus, ob/ob mice have a low level of sympathetic activity but also a high level of bone resorption [28] although adrenergic agonists stimulate bone resorption in mouse calvarium [24] and RANKL expression in MC3T3-E1 osteoblastic cells [29]. The high level of bone resorption in ob/ob mice may result from the very low level of expression of cocaine amphetamine regulated transcript (CART), a neuromediator involved in leptin-dependent appetite regulation. CART inhibits the regulation of bone resorption by modulating the expression of RANKL. Taken in concert, available data strongly suggest that leptin may act both directly and indirectly on bone tissue by modulating the activity of osteoblasts and osteoclasts. In an attempt to reconcile the apparently contradictory results obtained so far, we hypothesized that bone tissue effects of leptin result from a balance between two pathways, a central inhibitory pathway acting via the hypothalamic nuclei and β-adrenergic system and a peripheral stimulating pathway triggered when leptin binds to its specific receptors expressed by osteoblastic cells. Studies are needed to investigate this hypothesis, to determine the relative roles of each pathway, and to discover how each pathway comes into play in various energy-balance situations. References [1] [2]
Spiegelman BM, Flier JS. Obesity and the regulation of energy balance. Cell 2001;104:531–43. Henry BA, Goding JW, Alexander WS, Tilbrook AJ, Canny BJ, Dunshea F, et al. Central administration of leptin to ovariectomized ewes inhibits food intake without affecting the secretion of hormones from the pituitary
[3] [4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15] [16] [17]
[18] [19]
[20]
[21]
[22]
[23]
[24]
gland: evidence for a dissociation of effects on appetite and neuroendocrine function. Endocrinology 1999;140:1175–82. Thomas T. Leptin: a potential mediator for protective effects of fat mass on bone tissue. Joint Bone Spine 2003;70:18–21. Thomas T, Gori F, Khosla S, Jensen MD, Burguera B, Riggs BL. Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes. Endocrinology 1999; 140:1630–8. Reseland JE, Syversen U, Bakke I, Qvigstad G, Eide LG, Hjertner O, et al. Leptin is expressed in and secreted from primary cultures of human osteoblasts and promotes bone mineralization. J Bone Miner Res 2001; 16:1426–33. Cornish J, Callon KE, Bava U, Lin C, Naot D, Hill BL, et al. Leptin directly regulates bone cell function in vitro and reduces bone fragility in vivo. J Endocrinol 2002;175:405–15. Lee YJ, Park JH, Ju SK, You KH, Ko JS, Kim HM. Leptin receptor isoform expression in rat osteoblasts and their functional analysis. FEBS Lett 2002;528:43–7. Takahashi Y, Okimura Y, Mizuno I, Iida K, Takahashi T, Kaji H, et al. Leptin induces mitogen-activated protein kinase-dependent proliferation of C3H10T1/2 cells. J Biol Chem 1997;272:12897–900. Iwaniec UT, Shearon CC, Heaney RP, Cullen DM, Yee JA. Leptin increases number of mineralized bone nodules in vitro. Bone 1988;23 (Suppl):S212. Gordeladze JO, Drevon CA, Syversen U, Reseland JE. Leptin stimulates human osteoblastic cell proliferation, de novo collagen synthesis, and mineralization: Impact on differentiation markers, apoptosis, and osteoclastic signaling. J Cell Biochem 2002;85:825–36. Burguera B, Hofbauer L, Thomas T, Gori F, Lassam J, Laasko K, et al. Leptin reduces ovariectomy-induced bone loss in rats. Endocrinology 2001;142:3546–53. Bai Y, Zhang S, Kim KS, Lee JK, Kim KH. Obese gene expression alters the ability of 30A5 preadipocytes to respond to lipogenic hormones. J Biol Chem 1996;271:13939–42. Steppan CM, Crawford DT, Chidsey-Frink KL, Ke H, Swick AG. Leptin is a potent stimulator of bone growth in ob/ob mice. Regul Pept 2000;92: 73–8. Ducy P, Amling M, Takeda S, Priemel M, Schilling AF, Beil FT, et al. Leptin inhibits bone formation through a hypothalamic relay: a central control of bone mass. Cell 2000;100:197–207. Lorentzon R, Alehagen U, Boquist L. Osteopenia in mice with genetic diabetes. Diabetes Res Clin Pract 1986;2:157–63. Foldes J, Shih MS, Levy J. Bone structure and calcium metabolism in obese Zucker rats. Int J Obes Relat Metab Disord 1992;16:95–102. Mathey J, Horcajada-Molteni MN, Chanteranne B, Picherit C, Puel C, Lebecque P, et al. Bone mass in obese diabetic Zucker rats: influence of treadmill running. Calcif Tissue Int 2002;70:305–11. Schilling A, Holzmann T, Rueger J, Karsenty G. Leptin regulates bone mass in rats. Bone 2001;28(Suppl):S88. Hamrick MW, Pennington C, Newton D, Xie D, Isales C. Leptin deficiency produces contrasting phenotypes in bones of the limb and spine. Bone 2004;34:376–83. Elefteriou F, Takeda S, Ebihara K, Magre J, Patano N, Kim CA, et al. Serum leptin level is a regulator of bone mass. Proc Natl Acad Sci USA 2004;101:3258–63. Takeda S, Elefteriou F, Levasseur R, Liu X, Zhao L, Parker KL, et al. Leptin regulates bone formation via the sympathetic nervous system. Cell 2002;111:305–17. Togari A. Adrenergic regulation of bone metabolism: possible involvement of sympathetic innervation of osteoblastic and osteoclastic cells. Microsc Res Tech 2002;58:77–84. Moore RE, Smith 2nd CK, Bailey CS, Voelkel EF, Tashjian Jr. AH. Characterization of beta-adrenergic receptors on rat and human osteoblast-like cells and demonstration that beta-receptor agonists can stimulate bone resorption in organ culture. Bone Miner 1993;23:301–15. Liu C, Grossman A, Bain S, Strachan M, Puerner D, Bailey C, et al. Leptin stimulates cortical bone formation in obese (ob/ob) mice. J Bone Miner Res 1997;12(Suppl 1):S115.
T. Thomas, A. Martin / Joint Bone Spine 72 (2005) 471–473 [25] Hamrick MW, Della-Fera MA, Choi YH, Pennington C, Hartzell D, Baile CA. Leptin treatment induces loss of bone marrow adipocytes and increases bone formation in leptin-deficient ob/ob mice. J Bone Miner Res 2005;20:994–1001. [26] Holloway WR, Collier FM, Aitken CJ, Myers DE, Hodge JM, Malakellis M, et al. Leptin inhibits osteoclast generation. J Bone Miner Res 2002; 17:200–9. [27] Martin A, de Vittoris R, David V, Moraes R, Begeot M, LafageProust MH, et al. Leptin modulates both resorption and formation while
473
preventing disuse-induced bone loss in tail-suspended female rats. Endocrinology 2005;146:3652–9. [28] Elefteriou F, Ahn JD, Takeda S, Starbuck M, Yang X, Liu X, et al. Leptin regulation of bone resorption by the sympathetic nervous system and CART. Nature 2005;434:514–20. [29] Takeuchi T, Tsuboi T, Arai M, Togari A. Adrenergic stimulation of osteoclastogenesis mediated by expression of osteoclast differentiation factor in MC3T3-E1 osteoblast-like cells. Biochem Pharmacol 2001;61: 579–86.
Research lecture
Bone metabolism and energy balance: role for leptin◊ Thierry Thomas *, Aline Martin Inserm E0366, Rheumatology Department, Saint-Etienne Teaching Hospital, Boulevard Pasteur, 42055 Saint-Etienne Cedex 02, France Received 5 October 2005; accepted 6 October 2005 Available online 25 October 2005
Keywords: Leptin; Osteoblast; Osteoclast; RANKL; Obesity
Both obesity and osteoporosis are major public health issues in their own right. Leptin seems to mediate the protective effects of fat mass on bone. This 16-kDa product of the ob gene is produced primarily by white adipose tissue, and its plasma levels are closely correlated with fat mass. Leptin has generated considerable interest as a marker for energy status. [1] Independently from the central appetite-regulating loop, leptin acts on most of the endocrine pathways not only via the hypothalamopituitary axis, but also directly on peripheral endocrine glands [2]. Leptin deficiency leads to multiple phenotypic abnormalities in addition to obesity, establishing a pleiotropic role for this hormone, which is involved in regulating many physiological processes including bone metabolism [3]. Thomas et al. [4] followed by other groups [5,6] showed that cells of osteoblast lineage, whether precursor stromal cells or more mature osteoblasts, constitute a target for leptin, as they express the long and short forms of the leptin receptor, whose activation generates a signal via STAT3 phosphorylation [7]. In vitro studies established that leptin induced MAPK-dependent proliferation of murine C3H10T1/2 multipotent stromal cells [8] and of osteoblasts at a more differentiated stage [6]. Furthermore, leptin enhances the osteoblastic differentiation of human stromal cells, inducing increased mineralization of the extracellular matrix. [4] Similar findings have been obtained with other cell models [5,9,10]. In vivo, intraperitoneal leptin injections reduced the bone loss caused by estrogen deprivation in ovariectomized rats [11]. In addition, daily systemic administration of leptin to sexually mature male mice *
Corresponding author. Tel.: +33 4 77 12 76 49; fax: +33 4 77 12 75 77. E-mail address: [email protected] (T. Thomas). ◊ Lecture held on the occasion of the 18th French Congress for Rheumatology. 1297-319X/$ - see front matter © 2005 Elsevier SAS. All rights reserved. doi:10.1016/j.jbspin.2005.10.005
was followed by a greater than 20% increase in mechanical bone strength [6]. These beneficial effects on bone may depend, at least in part, on the ability of leptin to reciprocally modulate stromal cell differentiation toward osteoblasts and adipose cells, inhibiting adipogenesis via a negative feedback loop operating in parallel with the osteoblast-stimulating effects [4,12]. However, in animals with leptin pathway abnormalities (absence of leptin or leptin-receptor mutations), the effects of leptin on bone described are conflicting and are at times inconsistent with the in vitro and in vivo effects discussed above. Steppan et al. [13] reported decreased bone mineral content (BMC) and bone mineral density (BMD) values at the whole body and femur of ob/ob mice, which lack leptin, suggesting a beneficial effect of leptin on bone. However, in a study by Ducy et al. [14] a high bone mass phenotype was found in ob/ob mice. Lorentzon et al. [15] reported that db/db mice lacking functional leptin receptors had osteopenia with thinning of the femoral cortex and loss of trabeculae compared to normal mice, whereas Ducy et al. [14] concluded that bone mass was noticeably increased in db/db mice compared to wild-type mice. Zucker fa/fa rats, which are obese and lack functional leptin receptors, were reported by Foldes et al. [16] and Mathey et al. [17] to have decreased BMC and BMD values at the total femur, femoral diaphysis and femoral metaphysis, compared to normal rats. On the other hand, Schilling et al. [18] reported a high bone mass phenotype in Zucker rats similar to that seen in ob/ob mice. These discrepancies may be partly ascribable to bone phenotype differences between the axial and the peripheral skeleton [19]. Ducy et al. [14] showed that intracerebroventricular leptin injections were followed by a decrease in bone density, both in ob/ob mice and in wild-type mice [20]. This leptin-dependent
472
T. Thomas, A. Martin / Joint Bone Spine 72 (2005) 471–473
central inhibition of bone formation is mediated by the sympathetic system [21] that acts directly on osteoblasts expressing the β2 adrenoceptor [22,23]. Other studies in ob/ob mice showed that intraperitoneal leptin induced a major increase in cortical bone formation [24] an increase in endosteal bone formation with a decrease in the concentration of bone marrow adipocytes [25] and correction of the osteopenia and bone growth deficiency characteristic of the ob/ob phenotype, compared to controls, despite decreases in food intake and body weight [13]. Leptin may control the activity of osteoclasts, which constitute another potential cell target. Leptin can modulate the RANKL/osteoprotegerin (OPG) ratio by inhibiting RANKL expression and stimulating OPG expression in preosteoblastic stromal cells [11] and circulating mononuclear cells [26]. There is conclusive evidence that the RANKL/OPG ratio is crucial to the control of osteoclastogenesis. RANKL expressed by osteoblastic cells binds to RANK at the surface of preosteoclasts and of osteoclasts at a more mature stage, stimulating their differentiation, maintaining their activity, and inhibiting their apoptosis. OPG, which is also expressed by osteoblasts, acts as a soluble receptor that prevents RANKL from binding to RANK. This dual effect of leptin, with inhibition of bone resorption and stimulation of bone formation, was recently confirmed in vivo in an animal model of immobility-induced osteoporosis, in which the RANKL/OPG ratio within bone tissue returned to normal [27]. Again, results from different models seem to contradict one another. Thus, ob/ob mice have a low level of sympathetic activity but also a high level of bone resorption [28] although adrenergic agonists stimulate bone resorption in mouse calvarium [24] and RANKL expression in MC3T3-E1 osteoblastic cells [29]. The high level of bone resorption in ob/ob mice may result from the very low level of expression of cocaine amphetamine regulated transcript (CART), a neuromediator involved in leptin-dependent appetite regulation. CART inhibits the regulation of bone resorption by modulating the expression of RANKL. Taken in concert, available data strongly suggest that leptin may act both directly and indirectly on bone tissue by modulating the activity of osteoblasts and osteoclasts. In an attempt to reconcile the apparently contradictory results obtained so far, we hypothesized that bone tissue effects of leptin result from a balance between two pathways, a central inhibitory pathway acting via the hypothalamic nuclei and β-adrenergic system and a peripheral stimulating pathway triggered when leptin binds to its specific receptors expressed by osteoblastic cells. Studies are needed to investigate this hypothesis, to determine the relative roles of each pathway, and to discover how each pathway comes into play in various energy-balance situations. References [1] [2]
Spiegelman BM, Flier JS. Obesity and the regulation of energy balance. Cell 2001;104:531–43. Henry BA, Goding JW, Alexander WS, Tilbrook AJ, Canny BJ, Dunshea F, et al. Central administration of leptin to ovariectomized ewes inhibits food intake without affecting the secretion of hormones from the pituitary
[3] [4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15] [16] [17]
[18] [19]
[20]
[21]
[22]
[23]
[24]
gland: evidence for a dissociation of effects on appetite and neuroendocrine function. Endocrinology 1999;140:1175–82. Thomas T. Leptin: a potential mediator for protective effects of fat mass on bone tissue. Joint Bone Spine 2003;70:18–21. Thomas T, Gori F, Khosla S, Jensen MD, Burguera B, Riggs BL. Leptin acts on human marrow stromal cells to enhance differentiation to osteoblasts and to inhibit differentiation to adipocytes. Endocrinology 1999; 140:1630–8. Reseland JE, Syversen U, Bakke I, Qvigstad G, Eide LG, Hjertner O, et al. Leptin is expressed in and secreted from primary cultures of human osteoblasts and promotes bone mineralization. J Bone Miner Res 2001; 16:1426–33. Cornish J, Callon KE, Bava U, Lin C, Naot D, Hill BL, et al. Leptin directly regulates bone cell function in vitro and reduces bone fragility in vivo. J Endocrinol 2002;175:405–15. Lee YJ, Park JH, Ju SK, You KH, Ko JS, Kim HM. Leptin receptor isoform expression in rat osteoblasts and their functional analysis. FEBS Lett 2002;528:43–7. Takahashi Y, Okimura Y, Mizuno I, Iida K, Takahashi T, Kaji H, et al. Leptin induces mitogen-activated protein kinase-dependent proliferation of C3H10T1/2 cells. J Biol Chem 1997;272:12897–900. Iwaniec UT, Shearon CC, Heaney RP, Cullen DM, Yee JA. Leptin increases number of mineralized bone nodules in vitro. Bone 1988;23 (Suppl):S212. Gordeladze JO, Drevon CA, Syversen U, Reseland JE. Leptin stimulates human osteoblastic cell proliferation, de novo collagen synthesis, and mineralization: Impact on differentiation markers, apoptosis, and osteoclastic signaling. J Cell Biochem 2002;85:825–36. Burguera B, Hofbauer L, Thomas T, Gori F, Lassam J, Laasko K, et al. Leptin reduces ovariectomy-induced bone loss in rats. Endocrinology 2001;142:3546–53. Bai Y, Zhang S, Kim KS, Lee JK, Kim KH. Obese gene expression alters the ability of 30A5 preadipocytes to respond to lipogenic hormones. J Biol Chem 1996;271:13939–42. Steppan CM, Crawford DT, Chidsey-Frink KL, Ke H, Swick AG. Leptin is a potent stimulator of bone growth in ob/ob mice. Regul Pept 2000;92: 73–8. Ducy P, Amling M, Takeda S, Priemel M, Schilling AF, Beil FT, et al. Leptin inhibits bone formation through a hypothalamic relay: a central control of bone mass. Cell 2000;100:197–207. Lorentzon R, Alehagen U, Boquist L. Osteopenia in mice with genetic diabetes. Diabetes Res Clin Pract 1986;2:157–63. Foldes J, Shih MS, Levy J. Bone structure and calcium metabolism in obese Zucker rats. Int J Obes Relat Metab Disord 1992;16:95–102. Mathey J, Horcajada-Molteni MN, Chanteranne B, Picherit C, Puel C, Lebecque P, et al. Bone mass in obese diabetic Zucker rats: influence of treadmill running. Calcif Tissue Int 2002;70:305–11. Schilling A, Holzmann T, Rueger J, Karsenty G. Leptin regulates bone mass in rats. Bone 2001;28(Suppl):S88. Hamrick MW, Pennington C, Newton D, Xie D, Isales C. Leptin deficiency produces contrasting phenotypes in bones of the limb and spine. Bone 2004;34:376–83. Elefteriou F, Takeda S, Ebihara K, Magre J, Patano N, Kim CA, et al. Serum leptin level is a regulator of bone mass. Proc Natl Acad Sci USA 2004;101:3258–63. Takeda S, Elefteriou F, Levasseur R, Liu X, Zhao L, Parker KL, et al. Leptin regulates bone formation via the sympathetic nervous system. Cell 2002;111:305–17. Togari A. Adrenergic regulation of bone metabolism: possible involvement of sympathetic innervation of osteoblastic and osteoclastic cells. Microsc Res Tech 2002;58:77–84. Moore RE, Smith 2nd CK, Bailey CS, Voelkel EF, Tashjian Jr. AH. Characterization of beta-adrenergic receptors on rat and human osteoblast-like cells and demonstration that beta-receptor agonists can stimulate bone resorption in organ culture. Bone Miner 1993;23:301–15. Liu C, Grossman A, Bain S, Strachan M, Puerner D, Bailey C, et al. Leptin stimulates cortical bone formation in obese (ob/ob) mice. J Bone Miner Res 1997;12(Suppl 1):S115.
T. Thomas, A. Martin / Joint Bone Spine 72 (2005) 471–473 [25] Hamrick MW, Della-Fera MA, Choi YH, Pennington C, Hartzell D, Baile CA. Leptin treatment induces loss of bone marrow adipocytes and increases bone formation in leptin-deficient ob/ob mice. J Bone Miner Res 2005;20:994–1001. [26] Holloway WR, Collier FM, Aitken CJ, Myers DE, Hodge JM, Malakellis M, et al. Leptin inhibits osteoclast generation. J Bone Miner Res 2002; 17:200–9. [27] Martin A, de Vittoris R, David V, Moraes R, Begeot M, LafageProust MH, et al. Leptin modulates both resorption and formation while
473
preventing disuse-induced bone loss in tail-suspended female rats. Endocrinology 2005;146:3652–9. [28] Elefteriou F, Ahn JD, Takeda S, Starbuck M, Yang X, Liu X, et al. Leptin regulation of bone resorption by the sympathetic nervous system and CART. Nature 2005;434:514–20. [29] Takeuchi T, Tsuboi T, Arai M, Togari A. Adrenergic stimulation of osteoclastogenesis mediated by expression of osteoclast differentiation factor in MC3T3-E1 osteoblast-like cells. Biochem Pharmacol 2001;61: 579–86.